Control apparatus



Jan. 5, 1937. E. M. MILLER 2,066,413

CONTROL APPARATUS Filed April 28, 1930 Fig. 1

I NVfiNTOR ERNE5T M. MILLER ATTORNEXS Patentd Jan. 5, 1937 UNITED STATES PATENT OFFICE CON1EOL APPARAIUS Application April 28, 1930, Serlal No. 8,011

17 Claims.

'Ihis invention relates to improvements in burner apparatus control means, in which the apparatus to be controlled includes a bumer. combustion chamber, burner drait motor, igni- 5 tian and fuel supply and control means. The control of this invention includes means whereby ignition the fuel may be obtained; means whereby if flame is not produced when ignition and fuel is supplied the apparatus will cease to operate; means whereby ignition may be maintained for a predetermined length of time after production of flame, and then discontinued; means whereby ignition can be discontinued, but motor operation continued, until {lame is extinguished either by a call for less heat and normal shut-down of the motor, or by flame or electrical failure; and means providing delayed re-ignition aiter a shut-down, no matter what the cause.

Features of the invention include .specific as well as generic ideas of means.

Features and advantages of the invention will be set iorth in the description of the drawing forming a part of this application, and in said 25 drawing:

Figure 1 is a diagrammatic view illustrating the condition of the apparatus after activation on a call for heat;

Figure 2 represents the condition of the same system aiter flame has been produced, and before the ignition means 15 de-activated; and

Figure 3 represents the normal operating condition of the system after fiame has been produced. and after ignition has been rendered inoperative.

The circuit arrangement of each figure is identicai with that of every other, only the positions of the relays and contacts diier. The numerals have (in order to avoid confusing multiplication) ben applied in any figure only to those parts of the circuit which are active, but any missing number can be easily found by reference to another figure (see description of the operation).

Referring to the drawing, a thermal safety switch is provided for rendering the entire apparatus inoperative at the end of a predetermined time if flame is not prcduced. This device includes a switch 6, and a heating coil which causes the switch to open in a well known manner at the end 01 a predetermined time. The device is made operative simultaneously with ignition. A room thermostat includes elements W, B, R. A time switch includes a bimeta1lic thermal element I2 controlling contacts Il and I3, along with the 35 heating element 56. This time switch functions when sufliciently cold to close the contact Il which is in the starting circuit to coil I6 of relay No. I. The starting circuit includes element l2,

in series with switch 6, and with coil l5. Ele- 0 ment l2 is here shown as a bimeta1lic arm. utiliz ed as a conductor. Other equivalent devices may be used. 'Ihis switch also iunctions to close a holding circuit for relay No. i, which includes coils ll8 and additionally tunctions when sutflciently hot and at the end of a predetermined time to open both contacts lii3 (respectively starting and holding contacts for relay No. I) and cause them to remain open under the heating action of the coil (and after opening of relay No. l) as long as the apparatus is operative. When there is a call for less heat by the room thermostat the whole device 1s rendered inoperative. and

cannot be started until the time switch l2, as the result ci a cooling action again closes the contact Il. Relay No. i controls its own holding contact 20 which contact 15 closed when the relay is energized, and also controls a contact 2l in the starting circuit of coil 58 01 relay No. 2. Relay No. I when energized also closes contacts 22 and 23 respectively energizing ignition means and burner motor. Numerai 43 indicates the coil ci relay No. 3 and this coil is energized when the contact 40 closes. This contact is thermaily controlled, in a manner not shown, and is part of what is well known as a pyrostat or an instrument which closes its contact in response to production of flame at the burner, and usually placed in the stack. The function oi relay No. 8 is to break the starting circuit to relay No. I and to complete a starting circuit to relay No. 2 on production of flame. Relay No. 2 is energized substantially simultaneously with the energizatian of relay No. 3.

Relay No. 2 controls contacts 60, SI and 62. Contact 60 controls a holding circuit for relay No. I which does not include the heating coil I5 of the thermal safety switch. When contact 60 closes, coil [5 is thereiore shunted out. Contact 6! is in the holding circuit for relay No. 2, and contact 62 is a second contact which controls the motor and maintains it in operative condition, after opening of relay No. I and contacts 22-23 controlled thereby. Suitable ignition means is indicated at 38 and a suitable bumer mater at 34.

In the embodiment of the invention shown in the drawing, the function 01 No. i relay is to activate ignition and motor, establish a holding circuit for itself (which can be opened by either the thermal satety or time switch) and close 9. contact in the starting circuit for No. 2 relay. The function of No. 3 relay is, on production of flame, to close a contact which is in both starting and holding circuits for No. 2 relay, and to open a contact which is in the starting circuit for No. I relay. Energization cf No. 2 relay causes heat to be delivered to coil 56 of the time switch, shunts out the coil li 0! the thermal safety switch, establishes a holding circuit for itself, and 'for relay No. I through the heating coil of the time switch. The function of the time switch (when sufllciently cold) is to close the starting circuit for No. I relay, which when energized activates ignition and burner motor (when the room thermostat is closed) and later, when sufiiciently hot, breaks the holding circuit for No. I relay to render ignition inoperative.

Operation Assuming a call for heat (sec Figure 1) and closure 01 contacts B and W by R et the room thermostat. Relay No. i will be energized through the following circuit: secondary 4, conductor 5, switch 6, T, W, 13,6, contact 9, Il), contact thermal element of the time switch or its equivalent, contact I3, I4, heating coil l5 of the thermal saety switch, il, coil l6 of relay No. i, il to the opposite side of the transformer 4. Energization cf relay No. I results in the closure of four contacts, to-wit: 20, 2|, 22 and 23. Contact 2! is a holding contact for relay No. i and the holding circuit may be traced from the transformer 4, t0 R et the room thermostat, 24, 25, contact 20, 26, thermal element 12 of the time switch, contact i3, i4, and thence through heating coil I5, I1, relay coil I6, I1, to the opposite side of the transformer 4. Contact 2l is in the starting circuit for relay No. 2 and is closed on closure of No. i relay. Contact 22 establishes a circuit for the motor as follows: hot line l, 30, 3l, 22, '32, 33, motor 34, 35 to ground line 2. Contact 23 establishes a circuit for the ignition means as follows: line 1, 30, 36, 23, 31, ignition 38, 39 to ground line 2. After closure of relay No. I further operation of relays No. I and No. 2 is controlled through WR of the thermostat. Contact 2l controlled by relay No. I is in the starting circuit for relay No. 2 and it is thereiore seen that relay No. 2 can never close unless No.

I relay is energized,

Ignition means and the burner motor are now operative, and if combustion does not taire place at the end of a predetermined time saiety switch 6 will be opened due to the continued heating of element i5, circuit for relay No. i will be opened and contacts 20, 2l, 22 and 23 will be opened, thus de-activating ignition means and burner motor.

Under normal conditions, however, fiame will be produced at the end of a few seconds, and thermally controlled contact 40 will close, energizing coil 43 of relay No. 3 (sec Figure 2). As a result of this energization, starting contact 9 for No. I relay will be opened, starting contact 45 for relay No. 2 will be closed, and relay No. 2 will be substantially immediately energized through the following circuit: 4, 5, 6, 1, W, R, 24, 56, 45, 5l, 53, 2l, 54, 55, heating coil 56 of the time switch, 51, coil 58 of relay No. 2, 59, 11 to 4. Therefore, when flame is produced, relay No. 3 is energized, and then substantially immediately thereafter relay No. 2 is energized, as Well as heating coil 56 of the time switch.

With the closure of No. 2 relay, contact 60 of a shunt circuit is closed by means of which the coil [5 of the thermal saiety switch is shunted out or rendered inoperative, but the holding circuit for No. i relay is maintained. A150 by closure of No. 2 relay, a holding contact 6l for said relay is closed. A150 motor contact 62 is closed so that when No. I relay opens, whereby in opening contact 22, the motor will not be deenergized.

The holding circuit for relay No. i does not now include heating coil l5, but is now as follows: 4, 5, 6, 1, W, R, 24, 25, 20, 26, I2, I3, 14, 63, 60, 64, I6, I1 to 4. It will be notcd that this holding circuit for No. i passes through a contact controlled by No. l as well as a contact 60 controlled by No. 2 relay.

The holding circuit ior No. 2 relay is as tollows: 4 5, 6, 1, W, R, 24, 56, 45, 5|, 6l, 61, 5.5, 56, 51, coil 56, 59, il to 4. It will be notcd that this holding circuit passes through contact 45 et relay No. 3, contact 6| of relay No. 2 and heating coll 56 of the time switch.

Flame is now produced, but ignition is still active and will remain active for a predetermined period of time as controlled by the time switch [2. This period corresponds to the time required for the element 12 to move away from contact l3. after energization of heating coil 56, which resulted from energization of relay No. 2. It will be notcd that the coil 56 is in both starting and holding circuits for relay No. 2, but the holding circuit for No. 2 as a shunt, does not include contact 2l of relay No. I. Thereiore, when time switch contact l3 is broken and relay No. I and contact 21 open, coil 56 remains energized, as long as fiame is produced.

Continuing the operation:

All three relays are now energized, ignition and motor are energized, all contacts except the starting contact 9 for relay No. I are closed, and post-ignition energization will continue for a predetermined period of time. The timing switch now moves to the right and at the end of a predetermined time for which it is set, contact l3 is broken, and No. I relay drops out, breaking its own holding contact 20, and starting contact 21 et No. 2 relay circuit, and opening the ignition and motor contacts which are controlled by relay No. I. Ignition is thus de-actlvated, but motor operation continues.

Relays Nos. 2 and 3 (sec Figure 3) are now operative and the device is in what is lmown as the normal operative condition, that is heat is being delivered, and will be delivered until the thermostat element R breaks at W. It will be notcd that until this break occurs the heating coil of the time switch remains energized and the thermal element of the time switch remains in such a position that contacts il and I3 are open. This holding circuit for relay No. 2 has been previously traced.

After the call for heat has been satisfled, the

opening at RW renders the apparatus again inoperative, closes the starting contact 6 for relay No. I. However, it will be notcd that no restart 01 the apparatus can take place until after the predetermined time, required for the thermal element l2 of the time switch to move as the result of a cooling movement to the initial position, has transpired. At the end of this period, contacts Il and l3 are again closed, thereby again completing the starting circuit for relay No. I, if contacts B, W, R, are making. This is a testure of the invention. This delayed return to starting position prevents re-ignition. in presence of residual and explosive material in the combustion chamber.

In this embodiment oi! the invention, the thermal safety and time switches are in series in the starting circuit, which is energized on closure of the room thermostat. In case fiame is obtained, No. 3 relay pulls in and establishes a starting circuit for relay No. 2 (a ieature) and No. 2 relay then closes and establishes its own holding circuit. Both holding and starting circuits of relay No, 2 pass through the contact 45 controlled by No. I relay. The starting circuit for relay No. 2 la controlled by relay No. i. The net result is that No. 2 reiay cannot close uniess relays No. i and No. 8 have previousiy closed. Thereiore relay No. 2, which controis the burner motor or fuel feed during the normal running period, can be opened at any time aiter the ignition period. by reiay No. 3 which opens as the result of flame faiiure, and therefore the burner can be immediateiy shut down at any time after the ignition period, as the resuit ot flameiailure. On the other hand. during ignition period the fuel feed apparatus la operatively maintained independently oi reiay No. 2 by relay No. I. so that fuel and ignition can be supplied for a limited period of time whether or not flame is present.

The device oi! the present invention, therefore. provides means whereby ignition means is made operative before and atter flame production. The device aise provides means whereby there is a timed period between a shut clown et the apparatus due to opening of reiay No. 2, and reenergization 01 No. I reiay. 'Ihis delay sateguards against puits or explosion due to the ignition ct accumuiated vapors, should the flame be extinguished prematurely or should the apparatus bc stopped and started in quick succession, due to tampering with the room thermostat. An intervai of approximately ninety seconds or more must eiapse between the shut down oi the burner apparatus, and reciosing contacts iiil due to cooling motion of element i2.

It will also be noted that when relay No. 2 is energized the coil i5 of the thermal safety switch 6 is shunted out by contact 60, which is in the holding circuit of relay No. i. It will further be noted that contact 40 must be open and therefore relay No. 3 must be de-energized and contact 9 ciosed before relay No. i can be energized. The starting circuit for rela y No. 2 passes oniy through contact W 01 the room thermostat, and not through contact B.

An important feature is that contact 40 must be opened and therefore contact 9 closed, before the burner can start. This is important, because if the circuit to contact 40 should be shorted, either accidentaily or intentionaily, or should it stick and not open, it will be impossible for reiay No. 3 to drop out, and therefore contact 9 cannot close and the burner apparatus cannot be started until after inspection and repair. This' arrangement makes it necessary for the pyrostat contact 40 to check itseif for safety after each operation.

Another important feature which is again referred to is the deiayed closing of contacts H and l3 01 the time switch due to the cooling motion et the thermal element of the switch. With this arrangement, ignition cannot be restarted, after fiame extinguishment, except at the end of a time period of sufficient duration to allow dissipation of accumuiated explosive tire-pot gases. Thus explosion is prevented. Moreover, if the flame should be extinguished prematurely with the burner in normal running position, the contact 40 will open de-energized coi] 43 01 relay No. 3 and thereby breaking contact 45 which wiil cause reiay No, 2 t0 drop out and break the circuit to the burner motor by opening contact 62. Only a, few seconds will elapse between the extinguishment of the flame and the opening of the burner motor circuit and any vapors generated in the meanwhile will have ample opportunity to escape from the combustion chamber before the time switch can close its contacts IIII to obtain a restart et the apparatus. Upon power tailure alter successtul ignition, relays Nos. 2 and I will be de-energized. If power is resumed prior to the opening of pyrostat Ifl. relay No. 2 will be energized. Contact 9 will 5 therefore be open, as well as contacts H and I! and, thereiore, reiay No. I cannot be energized, to re-energize ignition and motor. A re-start cannot, thereiore, be had until the pyrostat Il has opened (to close contact 0) and until the thermostat 1! has cooled sufliciently to close contacts il and II. v

To recapituiate: Alter tuming on the burner motor, and ignition simultaneously, the device operates to maintain ignition until flame is produced. and then to maintain ignition for an additional predetermined period, which is adjustabie. In case of flame faiiure the present device shuts the burner apparatus down upon opening of the fiame responsive device 40, which contact ordinariiy opens at about ten seconds (very quick for a device of this klnd). In devices of other types. the burner was not shut down until the thermal saiety completed its timing period which was ordinarily one and une-hait minutes as compared with ten seconds in the present device. After flame tailure and shut down, the present control makes the burner to stand idle for a period suflicient for explosive gases to be drawn off by the natural draft of the furnace. In the present device this period is from one and one-haif to two and one-haif minutes. The thermostat is aiwas in command of the burner apparatus to shut down whether it isbeing main tained in operative condition by relay No. l or relay No. 2 or by both relays.

I claim as my invention:

1. An apparatus for controliing combustiom including as elements, an igniter and motor and means for controlling them for energization on a call for heat, means for independently controllin the motor to maintain its energization, thermal means responsive to production of combustion, means for timing an ignition period, and circuit connections and contacts so interconnecting the aforementioned elemehts that said combustion responsive means causes operation of said second named means to maintain motor energization and initiates timing action of the timing means after successiul ignition, thereby to con- 50 tinue ignition encrgization during the timing period, said timing means at the end of a timing period eifecting a de-activation of the first named means.

2. An apparatus for controlling combustion including as elements, an igniter and motor and means for controiling them for energization on a call for heat, means for independently controliing the motor to maintain its energization, thermal means responsive to production of combustion, means for timing an ignition period, and circuit connections and contacts 50 interconnecting the aiorementioned elements that said combustion responsive means causes operation of said second named means to maintain motor encrgization and initiate timing action of the timing means after successiui ignition, and continues ignition energization during the timing period, said timing means at the end of a timing period deenergizing said first named means to rie-activate the igniter, while the second named means maintains motor energlzation, and said timing means at the end of the ignition timing period being maintained operative, and being constructed to require a time period to retum to inoperativc position 50 as to prevent re-energization 01 the igniter after fiame extinguishment, except at the end of a timed period.

3. A device of the class described including an igniter, a fuel motor, a first relay operable when energized to energize the igniter and motor, and also to close first and second contacts, a second relay operable when energized to energize the motor and also close :1 contact, a combustion responsive device operable in response to combustion to open a first and close a second contact, a thermal timer switch operable when heated to open rst and second contacts, 3. heater for the thermal timer switch, a starting circuit for the flrst relay including therein the first contact et the combustion responsive device and both contacts of the timer switch, a holding circuit for the first relay including therein the first contact of the first relay and the second contact of said timer switch, a starting circuit for the second relay including therein the second contact ci the combustion responsive device, the second contact of the first relay and the heater of the timer switch, and a holding circuit for said second relay including therein the second contact of said com bustion responsive device, the contact of said second relay, and said heater.

4. A device of the class described including an igniter, a fuel motor, a first relay operable when energized t0 energize the igniter and motor and also to close first and second contacts, a second relay operable when energized to close 9. circuit to the motor and also close a contact, a combustion responsive device operable in response to combustion to open a flrst and close a second contact, a thermal safety switch and hcater therefor, a thermal timer switch operable when heated to open first and second contacts, a heater for the timer switch, a starting circuit for the first relay including therein said safety switch, the first contact et the combustion responsive device, both contacts et the timer switch, and the heater of said safety switch, a holding circuit for the first relay including therein said safety switch, the first contact of the first relay, the second contact of said timer switch, and the heater of said safety switch, a starting circuit for the second relay including therein said saiety switch, the second contact of the combustion responsive device, the second contact of the first relay and the heater of said timer switch, and a holding circuit foi said second relay including therein the second contact of said combustion responsive device, the contact of said second relay, and said hcater of the timer switch.

5. In a system of the class described including an igniter, a fuel motor, a first relay operable when energized to control igniter, and motor, a second relay operable when energized to control the motor, a combustion responsive device operable only when flame is absent to permit energization of the first relay. and further operable only when flame is present to permit energization of the second relay, a timer switch including a thermal element and a heater, a room thermostat, and circuit connections and contacts controlled by the room thermostat, timer switch, relays and combustion responsive device, and so arranged that on initial closure of the room thermostat with said combustion responsive device in its inoperative position in absence of combustion the first relay is energized through a circuit which has been closcd by the timer switch as result of the cooling motion of the thermal element to energize igniter and motor, and so that only aiter production of combustion and after said combustion responsive device moves to its operative position the second relay is energized to close a maintaining circuit for the motor, and the heater is energized to cause the timer switch to open after a predetermined time period ollowing successful combustion to de-energize the first relay and igniter, heater energization being maintained while the second relay is closed, so that on combustion failure after successful combustion causing said combustion responsive device to return to inoperative position, the first relay can only be energized after a timed interval as a result of closing of the timer switch by cooling motion of its thermal element.

6. In a system of the class desCribed including an igniter, a fuel motor, a first relay operable when energized to control igniter and motor, 9. second relay operable when energized to control the motor, a combustion responsive device, a timer switch and a heater for the timer switch, a room thermostat, and circuit connections and contacts controlled by the room thermostat, timer switch, relays and combustion responsive device, and so arranged that on initial closure 01 the room thermostat and only in absence 01 combustion with said combustion responsive device.

in inoperative position, the first relay is energized through 3. circuit which has been closed by the timer switch, and so that on production 01 combustion and after said combustion responsive device moves to its operative position, the second relay is energized, and also the heater for the timer switch, to cause the timer switch to open after a predetermined time period t0 de-energize the first relay and igniter, and so that heater energization is maintained while the second relay is closed.

7. A device ci the class described including an igniter, a fuel motor, flrst electrically operable means operable when energized to control igniter and motor, second electrically operable means operable when energized to control the motor, a combustion responsive device, a thermal timer switch and a heater for the timer switch, a room thermostat, and circuit connections and contacts controlled by the electrically operable means and combustion responsive device, timer switch and room thermostat, and so arranged that on initial closure of the room thermostat and in absence of combustion with said combustion responsive device in inoperative position the motor and isniter controlling means is energized through a circuit which passes through the timer switch, and so that only on production of combustion and after said combustion responsive device moves to its operative position, the second electrically operable means is energized to close a maintaining circuit for the motor, and also the heater is energized to cause the timer switch to open after a predetermined time period, to deenergize the first electrically operable means and igniter, and so that heater energiztion is maintained while the second electrically operable means is energized.

8. A system of the class described, comprising. in combination, an elcctrical fuel supply controlling device, electrically controlled means for igniting the fuel supplied by said device, a tirst switching mechanism in circuit with the fuel supply controllng device and electrically controlled ignition means, a relay for operating said switching mechanism, a. second switch in a parallel circuit for the fuel supply controlllng device, a

second relay for operating the second switch, an electrical timer, a timcr switch, a main control, 3. circuit for the first relay inciuding the timer switch and main controi, a combustion responsive switch, and a circuit arrangement controlled by the main control and combustion responsive switch for simuitaneousiy energizing the second rciay and the eiectrical timer.

9. A system of the class described, comprising, in combination, an eiectrical fuel supply controlling device, eiectricaily controiied means for igniting the fuel supplied by said device, a first switching mechanism in circuit with the fuel suppiy controlling device and electrically controlied ignition means, a relay for operating said switching mechanism, a second switch in a parallei circuit for the fuel suppiy controlling device, a second reiay for operating the second switch, a thermostatic switch, an eiectric heating element thereior, a main control, a circuit for the first relay including the thermostatic switch and main contre], a combustion responsive switch, and a circuit arrangement controlled by the main controi and combustion responsive switch for simultaneously cnergizing the second reiay and the electric heating eiement for the thermostatic switch.

10. A system of the class described, comprising, in combination, an electrical device for con troliing the supply of fuel to a burner, electricaliy controlled ignition means for igniting the fuel supplied to the burner, switching machanism in circuit with the fuel supply controlling device and ignition means, a first relay for operating said switching mechanism, a second switch in a parallel circuit for the fuel supply controlling device, a second relay for operating the second switch, an electro-thermal safety switch for rendering the entire system inoperative upon continued fiow of current therethrough, a main control, an electrical timer, a timer operated switch, an energizjng circuit for the first relay and eiectro-thermal safety switch including the main control, safety switch and timer operated switch, a combustion controlled switch, a circuit for the second reiay and the eiectricai timer including the main controi, safety switch and combustion controlled switch, and means controlied by the combustion contrciied switch for preventing operation of the safety switch to render the system inoperative if combustion is successul.

11. A system of the class described, comprising, in combination, an electrical device for controlling the supply of fuel to a burner, electrically controlled ignition means for igniting the fuel supplied to the burner, switching mechanism in circuit with the fuel suppiy controlling device and ignition means, a first relay for operating said switching mechanism, a second switch in a parallel circuit for the fuel supply controlling device, a. second relay for operating the second switch, an electro-thermal safety switch for rendering the entire system inoperative upon continued fiow of current therethrough, a main contro1, a thermostatic timing switch, an electrical heater therefor, an energizing circuit for the first relay and electro-thermal safety switch inciuding the main controi, timing switch, and safety switch, a combustion responsive switch, a circuit for the second relay and the electrical heater including the main control, safety switch and combustion responsive switch and means controlled by the combustion responsive switch ior preventing operation of the safety switch to render the system inoperative if combustion is successfu].

12. An oil burner control having a motor driven fuel-supply means, ignition means for said fuelsupply means, means for energizing said motor driven fuei-supply means, means for de-energizing said ignition system upon establishing combustion conditions and other means for rendering said ignition de-energizing means inoperative a predetermined period of time after combustion is estabiished.

13. A control for a combustion heating device, naving a fuel-supply means, an igniter for the fuel, a. device for rendering said fuel-supply means and igniter operative to establish combustion and means for rendering said ignition inoperative a predetermned period of time after combustion is established.

14. An cil burner having a fuel-suppiy means, an ignition system therefor, means for controlling energizaticn of said fuel-suppiy means to establish combustion, means for controlling energization of said ignition system, means for maintaining said iuel-supply means energized and for deenergizing said ignition system upon establishing combustion, and a time-delay means cooperating with said ignition system control means for maintaining said ignition system energized for a predetermined period after combustion is estabiished.

15. An cil burner control means having a fuelsupply motor, an ignition system therefor, means for initiating ope ration of said motor and ignition system to establish combustion, a heat-responsive device for de-energizing said ignition system and maintaining said fuel-supply motor energized upon establishirig combustion and timedeiay means for rendering said heat-responsive device inefiective to de-energize said ignition system for a predetermined period after combustion is established.

16. An automatic control system for oil burners having an igniter comprising a thermal trip time switch arranged to de-energize said system, 3. heating coil for causing operation of said trip switch, 3, thermostat having contacts, a circuit for said heating coi] closed responsive to actuation of said contacts, means in said circuit actw ated responsive to actuation of said thermostat contacts for rendering operative said burner and igniter, means actuated responsive to combustion at the said burner for rendering said heating coi] inoperative, a thermal time switch, a second heating coii for causing actuation of the contacts of said time switch and a circuit for said second time switch heating coil, means for operatively encrgizing said second heating coi] circuit responsive t0 actuation of said combustion responsive means, said time switch being arranged to render said igniter operating means inoperative after a predetermined period.

17. In combination, an electricaliy operated fluid fuel burner having an electrically operable igniter, means for initiating operation.of said burner and igniter, a timing device for stopping operation of said igniter and means responsive to the presence of a flame at said burner to start said timing device in operation to stop igniter activity a predetermined time after said flame responsive means has operated.

ERNEST M. MILLER. 

